Enhancement and speed-up of carrier dynamics in a dielectric nanocavity with deep sub-wavelength confinement

TL;DR

This paper demonstrates that dielectric bowtie nanocavities with deep sub-wavelength confinement significantly enhance ultrafast carrier dynamics and nonlinear effects, enabling faster and more efficient optical devices.

Contribution

It provides the first experimental investigation of ultrafast carrier dynamics in topology-optimized silicon bowtie nanocavities with sub-12 nm dimensions, showing improved speed and nonlinear interactions.

Findings

Carrier generation rate is significantly enhanced by two-photon absorption.

Carrier diffusion time is reduced to below 1 ps, much faster than conventional cavities.

Enhanced parametric effects improve the extinction ratio in the cavity.

Abstract

The emergence of dielectric bowtie cavities enable optical confinement with ultrahigh quality factor and ultra-small optical mode volumes with perspectives for enhanced light-matter interaction. Experimental work has so far emphasized the realization of these nanocavities. Here, we experimentally investigate the ultrafast dynamics of a topology-optimized dielectric (silicon) bowtie nanocavity, with device dimensions down to 12 nm, that localizes light to a mode volume deep below the so-called diffraction limit given by the half-wavelength cubed. This strong spatial light concentration is shown to significantly enhance the carrier generation rate through two-photon absorption, as well as reducing the time it takes for the carriers to recover. A diffusion time below 1 ps is achieved for the bowtie cavity, which is more than an order of magnitude smaller than for a conventional microcavity. Additionally, parametric effects due to coherent interactions between pump and probe signals are also enhanced in the bowtie cavity, leading to an improved extinction ratio. These results demonstrate important fundamental advantages of dielectric bowtie cavities compared to conventional point-defect cavities, laying a foundation for novel low-power and ultrafast optical devices, including switches and modulators.